SimpleObjectTransfer.java

/*******************************************************************************
 * Copyright (c) 2000, 2008 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.gef.dnd;

import org.eclipse.swt.dnd.ByteArrayTransfer;
import org.eclipse.swt.dnd.TransferData;

/**
 * Holds on to the object being transferred in a field so that DropTargetListeners can
 * know what's being dragged before the drop occurs.  The object isn't converted to bytes,
 * so this Transfer will only work when dragging within the same instance of Eclipse. 
 * Subclasses should maintain a single instance of their Transfer and provide a static
 * method to obtain that instance.
 */
public abstract class SimpleObjectTransfer extends ByteArrayTransfer {

private Object object;
private long startTime;

/**
 * Returns the Object.
 * @return The Object
 */
public Object getObject() {
	return object;
}

/**
 * The data object is not converted to bytes. It is held onto in a field. Instead, a
 * checksum is written out to prevent unwanted drags across mulitple running copies of
 * Eclipse.
 * @see org.eclipse.swt.dnd.Transfer#javaToNative(Object, TransferData)
 */
public void javaToNative(Object object, TransferData transferData) {
	setObject(object);
	startTime = System.currentTimeMillis();
	if (transferData != null)
		super.javaToNative(String.valueOf(startTime).getBytes(), transferData);
}

/**
 * The data object is not converted to bytes. It is held onto in a field. Instead, a
 * checksum is written out to prevent unwanted drags across mulitple running. copies of
 * Eclipse.
 * @see org.eclipse.swt.dnd.Transfer#nativeToJava(TransferData)
 */
public Object nativeToJava(TransferData transferData) {
	byte bytes[] = (byte[])super.nativeToJava(transferData);
	if (bytes == null) {
		return null;
	}
	long startTime = Long.parseLong(new String(bytes));
	return (this.startTime == startTime)
		? getObject()
		: null;
}

/**
 * Sets the Object.
 * @param obj The Object
 */
public void setObject(Object obj) {
	object = obj;
}

}